Confined bed metal particulate heat exchanger

ABSTRACT

A recuperative heat exchanger is provided for the efficient transfer of heat between two fluids of differing initial temperatures. In a preferred embodiment, a cross-flow heat exchanger includes an array of parallel tubes that are further disposed within one or more beds of confined metal particulates confined by screens and through which a relatively cold fluid flows. A second relatively hot fluid is directed through the particulate beds in a direction perpendicular to the tube array. Because of the high thermal conductivity of the particulates, heat is conducted across the beds to walls of the tubes which comprise the walls of the confined beds in a direction substantially transversely to the fluid flow. In an alternative embodiment, a counter-flow heat exchanger preferably includes a number of adjacent beds of conductive particulates confined at their top and bottom by screens and on their sides by parallel solid plates. Adjacent plate beds are connected with plenums at opposite ends. A first relatively hot fluid flows between alternating beds in one direction and a second relatively cold fluid flows through alternating beds in an opposite “counter-flow” direction. In all alternative configurations of the heat exchanger, the relative temperatures of the fluids may be reversed.

[0001] This application is a continuation-in-part of application Ser. No. 08/756,865 filed Nov. 26, 1996, now abandoned.

TECHNICAL FIELD

[0002] The present invention relates generally to heat exchangers and, more particularly, to recuperative heat exchangers. The invention is specifically disclosed as a recuperative heat exchanger that includes a confined bed of metal particulates through which fluid is passed for the purpose of transferring heat to or from the walls of the bed.

BACKGROUND OF THE INVENTION

[0003] In many modern engineering applications, heat exchangers of various configurations are extensively utilized for transferring heat between fluids of different temperatures. During the past several years, various improvements have been made in the field of heat transfer that have not only improved the efficiency of heat transfer processes in general, but have increased the efficiency of the devices employing the improved processes as well.

[0004] Historically, the amount of heat transferred between two moving fluid streams has been enhanced by extending and maximizing the surface area of the partition that separates the two streams and that forms a heat exchange surface across which heat transfer may occur. In conventional fin-tube heat exchanger designs, several such surface area extensions have been utilized, including the addition of protrusions such as pins or fins that extend from the various flow tubes of the heat exchangers.

[0005] Although the addition of such extensions to the heat exchanger tubes has been successful in providing a larger area of heat exchange surface, there are several key disadvantages that have been realized in the manufacture and application of heat exchangers of this type. For example, in order to join the extensions or fins to the flow tubes of the heat exchanger, a relatively expensive vacuum brazing process typically must be used. Accordingly, the overall cost of manufacturing such a heat exchanger is increased. Further, the sizes of the extensions are necessarily restricted due to limitations of available space to accommodate the heat exchangers in a particular application. In order to reduce the amount of space required, fin-tube heat exchangers have been fabricated in a variety of configurations that have included space saving features such as corrugated fins, flattened fluid tubes and offset fins. Nonetheless, the effective heat exchange surface area is inherently limited in any conventional fin-tube heat exchanger by the amount of space available for the heat exchanger.

[0006] Another disadvantage of conventional fin-tube heat exchanger configurations which negatively impacts heat transfer efficiency is that a film temperature drop occurs between the gas and the extended surfaces of the fins. This temperature difference results from a resistance to heat conduction through a relatively stagnant boundary layer or film of the gas next to the flattened surfaces of the fins.

[0007] In an apparent attempt to overcome some of the limitations associated with conventional fin-tube heat exchangers, several heat exchangers, such as that disclosed in U.S. Pat. No. 3,306,353 (Burne), have been developed using a body of porous conductive material that encases the heat exchanger flow tubes. Used in place of conventional extensions or fins, the porous conductive body of the type generally used in the prior art heat exchangers includes numerous interconnected voids or apertures. These voids have a corresponding large number of faces that result in a relatively large heat dissipating surface area within a relatively small volume, as compared to traditional fin-tube configurations. Typically, such porous bodies for use in heat exchangers are formed by placing and compacting conductive metallic particles into an appropriately shaped confined space. Next, the loose particles are treated by sintering, welding, brazing or soldering to produce a metallic bond between the particles. As a result, the porous body becomes a unified whole that is also bonded after the sintering, brazing or similar process to the flow tubes and any other solid material around or within the body.

[0008] Although heat exchangers incorporating this sintered porous body design have achieved, as compared to conventional fin-tube heat exchangers, a greater surface area for dissipating heat per unit volume, such heat exchangers are not without their limitations. Similar to conventional fin-tube heat exchangers, the conductive particles in prior art porous body heat exchangers must undergo sintering, brazing, or some other expensive metallurgical treatment process in order to bond the particles together and form the porous body.

[0009] Thus, it is clear that a need exists for a heat exchanger that is inherently simple to fabricate without a need for either the complex stamping and stacking of fins, or substantial metallurgical processing such as brazing or sintering. Such an improved heat exchanger would be flexible in its design to meet flow, heat transfer, and space limitations which are difficult or expensive to obtain with conventional extended surface systems. Such a heat exchanger would be characterized by a zero film temperature drop, so that the heat dissipating material is essentially at the same temperature as the temperature of the fluid flowing through it in order to improve thermal conductivity and heat transfer efficiency.

SUMMARY OF THE INVENTION

[0010] It is therefore a primary object of the present invention to provide a heat exchanger capable of efficient heat transfer while simultaneously occupying a minimal amount of space.

[0011] It is another object of the invention to overcome the aforementioned described limitations and disadvantages in the heat exchanger prior art.

[0012] It is still an additional object of the invention is to provide a heat exchanger that is readily capable of being manufactured with increased economic efficiency.

[0013] It is yet another object of the invention to provide a heat exchanger that is characterized by a zero film temperature drop between the heat dissipating material and the fluid which flows therethrough.

[0014] It is yet another object of the invention to provide a heat exchanger that is capable of being fabricated without extensive brazing, sintering, or welding.

[0015] It is still another object of the present invention is to provide a heat exchanger that includes a confined bed of conductive particulates through which fluid may flow and in which heat is readily transferred in a transverse direction to gas flow to the walls of the confining bed.

[0016] It is yet another object of the present invention to provide a heat exchanger characterized by flexible design capable of being constructed in various shapes and sizes that are not feasible with conventional fin surface systems, so as to meet unique space and performance requirements.

[0017] It is yet another object of the present invention to provide a heat exchanger with heat dissipating material that is essentially at the same temperature as the temperature of the heat exchange fluid flowing through it in order to improve heat transfer efficiency.

[0018] Additional objects, advantages and other novel features of the invention will be set forth in part in the description that follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned with the practice of the invention.

[0019] To achieve the foregoing and other objects, and in accordance with one aspect of the present invention as described herein, a recuperative cross-flow heat exchanger is provided wherein an array of parallel tubes through which a first fluid (which can be a liquid or a gas) flows are disposed within a bed of conductive metal particulates confined by appropriate screens. A second fluid flows through the confined bed perpendicular to the tube array. Because of their high thermal conductivity, the conductive metal particulates very closely assume the temperature of the fluids flowing by them resulting in high heat transfer efficiency. There is essentially a zero film temperature drop between the heat dissipating material and the fluid which flows therethrough. Heat is conducted across the confined bed of metal particulates to the walls of the confined bed in a direction substantially transverse to the fluid flow.

[0020] In an alternative embodiment of the present invention, a gas/gas counter-flow heat exchanger is provided in which the spaces between a plurality of spaced pairs of parallel plates, or side walls, are filled with conductive metal particulates to form“parallel plate beds.” Corresponding ends of each of the pairs of plates that form walls of a “parallel plate bed” are connected to a plenum. Adjacent pairs of plates are connected with plenums at opposite ends. As a result, a first gas stream flows between alternating pairs of plates in one direction, and a second gas stream flows through the other sides of alternating pairs of plates in opposite direction. The plates are enclosed at the bottom and top by solid plates and at the ducting ends by screen.

[0021] In an alternative embodiment of the counter-flow heat exchanger, a gas/fluid counter-flow heat exchanger is provided similar to the gas/gas counter-flow arrangement, wherein alternating parallel plate beds are filled with conductive metal particulates through which gas flows. Adjacent to each parallel bed containing particulates, is disposed at least one parallel plate bed through which fluid flows in a direction counter to the direction of the gas flow in the adjacent beds. Preferably, the fluid flows through an array of substantially parallel tubes disposed within each alternating parallel plate bed.

[0022] Still other objects of the present invention will become apparent to those skilled in this art from the following description and drawings wherein there is described and shown a preferred embodiment of this invention in one of the best modes contemplated for carrying out the invention. As will be realized, the invention is capable of other different embodiments, and its several details are capable of modification in various, obvious aspects all without department from the invention. Accordingly, the drawings and descriptions will be regarded as illustrative in nature and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention, and together with the description and claims serve to explain the principles of the invention. In the drawing:

[0024]FIG. 1 is a perspective view showing one bed of confined conductive particulates in contact with two fluid flow tubes, used in a recuperative heat exchanger constructed according to the principles of the present invention;

[0025]FIG. 2 is a perspective view of a conventional fin-tube arrangement of prior art heat exchangers;

[0026]FIG. 3 is a perspective view showing an array of stacked parallel layers of superposed confined particulate beds, in contact with several fluid flow tubes, used to construct a cross-flow heat exchanger according to the principles of the present invention;

[0027]FIG. 4 is a perspective cross-sectional view of an alternative embodiment of the cross flow heat exchanger of the present invention showing a plurality of coaxial cylindrical beds of confined conductive particulates, in contact with several fluid flow tubes;

[0028]FIG. 5 is a perspective view of an alternative embodiment of a cross-flow heat exchanger constructed according to the principles of the present invention showing a bed of confined conductive particulates comprising a substantially conical shell in contact with several fluid flow tubes;

[0029]FIG. 6 is a cut-away top plan view of a further alternative embodiment of a cross-flow heat exchanger constructed according to the principles of the present invention showing a disc-shaped bed of confined conductive particulates in contact with a spiral-shaped fluid flow tube;

[0030]FIG. 7 is a perspective view showing a single bed of confined conductive particulates comprising a contoured shell, in contact with several fluid flow tubes, and used in a recuperative heat exchanger constructed according to the principles of the present invention; and

[0031]FIG. 8 is a view of a gas-gas counter-flow heat exchanger constructed according to the principles of the present invention that includes a plurality of parallel plate beds of confined conductive particulates in communication with a plurality of gas plenums;

[0032]FIG. 9 is a perspective view of a liquid-gas counter-flow heat exchanger constructed according to the principals of the present invention that includes a plurality of parallel plate beds of confined conductive particulates;

[0033]FIG. 10 is a cross-sectional view of a plate bed from a counter-flow heat exchanger including a folded bed of conductive particulates;

[0034]FIG. 11 is a cross-sectional view of an alternate embodiment of the plate bed of the heat exchanger of the present invention including a plurality of transverse spacers; and

[0035]FIG. 12 is a cross-sectional view of a plate bed of the heat exchanger of the present invention comprising compartmentalized flow-channels formed from double corrugated walls.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0036] Reference will now be made in detail to the present preferred embodiment of the invention, an example of which is illustrated in the accompanying drawings, wherein like numerals indicate the same elements throughout the views.

[0037] As will become apparent by reviewing the description below, the heat exchanger of the present invention is capable of heat transfer in situations requiring unique space and performance requirements. Additionally, the heat exchanger of the present invention is capable of being efficiently manufactured without extensive brazing, sintering or welding operations. Because of the design flexibility of the heat exchanger of the present invention, it may be constructed in various shapes and sizes in a minimal amount of space not feasible with conventional fin surface systems.

[0038] Referring now to the drawings, FIG. 1 illustrates a single bed 10 constructed of confined conductive particulates according to the principles of the present invention. Each bed 10 of confined conductive particulates 11 is preferably retained by a number of side walls 16. Preferably, one or more of the walls 16 comprises a screen material which may be of polyester, metal, or other conventional material. More preferably, one or more walls of each particulate bed comprises a solid wall in order to block fluid flow in certain directions and to encourage fluid flow in a predetermined direction. According to an important aspect of the present invention, each bed 10 is of a thickness that permits fluid to flow therethrough without substantial resultant pressure drop.

[0039] As depicted in FIG. 1, each bed 10 includes one or more tubes 14 longitudinally disposed within the particulates 11. Preferably, each tube has a sufficiently large area to permit fluid flow therethrough with a minimal pressure drop. Each tube 14 is preferably of substantially rectangular cross-section having one of its perimeter dimensions approximately the same as the thickness of the bed 10 in which it is disposed.

[0040] In operation, and as shown by direction arrows “B” in FIG. 1, a relatively cold heat exchange medium, or fluid, is supplied through the tubes 14. As it will be understood, while the relatively cold fluid traverses the tubes 14, it is in a heat exchange relationship with the conductive particulates 11 of bed 10. Further, as indicated by direction arrows “A” in FIG. 1, a second relatively hot heat exchange medium, or fluid, is supplied through the bed 10 in which the movement of the fluid is substantially perpendicular to the tubes 14 in a cross-flow relationship with the fluid in the tubes 14. The fluid B moving through tubes 14 can be either a liquid or a gaseous material, whereas fluid A would typically be a gaseous material. While the relatively hot fluid travels through the bed 10, it is in a heat exchange relationship with the tubes 14. According to an important aspect of the invention, and because the particulates 11 have significant thermally conductive qualities, heat is readily conducted from the relatively hot first fluid A across the bed 10 to the walls 15 of the tubes 14 in a direction (as indicated by arrows “Z”) substantially transverse to the direction of fluid flow A of the relatively hot fluid. It will be understood that the relative temperatures of the fluids could easily be reversed in which fluid A was at a temperature lower than fluid B, without departing from the principles of the present invention. In this circumstance, the direction of heat transfer indicated by the arrows “Z” would be reversed from that depicted in FIG. 1.

[0041] In a conventional prior art extended surface heat exchanger as shown in FIG. 2, heat is transferred from the relatively hot fluid (see direction arrow A₁) to fins 17 across a somewhat conductively resistant boundary layer or film of fluid adjacent to the fins 17. In contrast, the heat exchanger of the present invention is characterized by substantially negligible resistance to heat conduction between the particulate bed 10 and the relatively hot fluid A. As a result, the heat exchanger of the present invention is capable of transferring heat in a more efficient manner than traditional prior art extended surface heat exchangers.

[0042] Preferably, the conductive particulates 11 are comprised of metal flakes, produced by a rapid solidification process which produces a fine grain structured body. More preferably, the particulates 11 are comprised of aluminum flakes. Each flake preferably has a thickness of about 0.001 to about 0.02 inches and a length and width ranging from about 0.04 to about 0.15 inches. The bulk flake material has very high geometric surface area to unit volume ratio of about 50 in²/in³ to about 300 in²/in³ and a relatively low solidity fraction having a range of about 0.085 to about 0.35. As it will be understood, particulates 11 may be fabricated of various sizes for use in a conductive bed depending on the requirements of the particular application. Particulate size may be tailored to the particular application in order to provide a conductive bed that has efficient heat transfer qualities but that results in relatively small resultant pressure drop when a fluid moves through the particulate bed. The thermal conductivity of bulk aluminum flakes is about 200 times less than solid aluminum and about 30 times higher than air. Additionally, since the particulates are preferably not sintered or otherwise bonded, the choice of materials for the particulates is not restricted by the requirements of bondability. The aluminum flake material provides very high thermal conductivity within each flake, high voidage, high surface area to volume ratio and relatively good corrosion resistance. As a result, the aluminum flakes in each bed achieve substantially instantaneous temperature equilibrium.

[0043] It will be understood that, in addition to aluminum, it is within the scope of the invention to use other metals having similar properties, particularly metals such as stainless steel, when higher temperatures or corrosive fluids may be used. At very high temperatures, such as those encountered in a recuperative heat exchanger for the exhaust gases from a gas turbine engine, the particulates may be fabricated from such materials as iron-silicon alloys, and confined by screens and walls having high temperature tolerances. For example, high temperature screens and walls may be comprised of iron-nickel-chromium alloys, tungsten, or any other material having adequate high temperature tolerances.

[0044] As shown in FIG. 3, a heat exchanger, generally indicated by the reference numeral 20, is provided and preferably includes a “stack” of superposed parallel substantially rectangular beds 10 of confined conductive particulates. By way of non-limiting example, a stack of five superposed beds 10 is shown in FIG. 3. Each bed preferably has a thickness of about 0.3 in. to about 2.0 in. and preferably is spaced apart from other like beds by a distance of about 0.3 in. to about 2.0 in. The area of each bed 10 and the number of beds can be chosen by a designer to meet the requirements of a particular application, such as the rated capacity of the heat exchanger as well as size and shape operational constraints.

[0045] Passages 21 between the beds provide for the entrance and exit of a relatively hot fluid parallel to the beds as indicated by direction arrows “C”, as well as for flow of the relatively hot fluid across the depth of the beds 10 through the conductive particulates 11 as indicated by direction arrows “D”. In order to direct the flow of the relatively hot fluid along the path of direction arrows D, adjacent pairs of superposed beds may be linked by end plates 23 to block fluid flow in a direction parallel to the beds 10.

[0046] A second relatively cold fluid is supplied through the tubes 14 of the various beds 10 (see direction arrows E). As will be understood, while the relatively cold fluid is within the tubes 14, it is in a heat exchange relationship with the conductive particulates 11. Further, as indicated by direction arrows D in FIG. 3, some of the relatively hot heat exchange medium, or fluid, is supplied through the beds 10 substantially perpendicularly to the tubes 14 in a cross-flow relationship with the fluid in the tubes 14. While the relatively hot fluid is moving within the beds 10, it is in a heat exchange relationship with the tubes 14. According to an important aspect of the invention, and because the beds 10 of particulates 11 have significant thermally conductive qualities, heat is readily conducted from the relatively hot fluid across the beds 10 to the walls 15 of the tubes 14 in a direction substantially transverse to the direction of fluid flow of the relatively hot fluid. As described above, the heat exchanger 20 of superposed parallel beds of conductive particulates of the present invention is characterized by a substantially negligible resistance to heat conduction between the particulate beds 10 and the relatively hot fluid. As a result, the heat exchanger of the present invention is capable of transferring heat in a more efficient manner than traditional prior art extended surface heat exchangers. In addition, it should be appreciated that the confining screens should have mesh size small enough to prevent particulate loss from the bed, and should have mesh size large enough so as to provide minimum obstruction to the fluid flow. Notably, the heat exchanger of the present invention is non-fluidized in that it does not use fluidized beds of particulates that rely on particulates floating in the drag of the fluid for effective heat transfer. Instead, the confined particulates remain substantially stationary with respect to the walls of the bed and to each other when a fluid is directed through the bed. To reiterate, in the present invention, fluid moves through the bed of substantially stationary metal particulates. Because of the preferred size and shape of the particulates, there remains much void space between the particulates in the bed of particulates. Because of the preferred particulate dimensions, they are of a relatively large surface area and small mass and are essentially thermally at the same temperature as the fluid passing through the bed and essentially isothermal within themselves. Accordingly, the fluid in the bed of particulates are essentially isothermal. Notably, the same is true between the fluid and particulate bed at the walls of the bed.

[0047] Accordingly, and according to an important aspect of the present invention, heat is readily transferred through the bed and then to the walls of the bed with a large heat transfer coefficient. Such a configuration, coupled with appropriately configured metal particulates, advantageously results in only a minimal pressure drop when fluid passes through the particulate bed. It will be understood that the relative temperatures of the fluids could be easily reversed in which fluid D was at a temperature lower than fluid E, without departing from the principals of the present invention. In this circumstance, the direction of heat transfer indicated by the arrows Z would be reversed from that depicted in FIG. 3.

[0048] Unlike the conventional extended surface heat exchangers of the prior art, the beds 10 of the particulate bed heat exchanger may be configured essentially in an endless variety of shapes and geometric arrangements. For example, it will be understood, as shown in FIG. 7, that a bed of conductive particulates, generally indicated by the reference numeral 70, may comprise a relatively thin contoured shell 72, capable of fitting adjacent to a similarly contoured surface area. This flexibility of particulate bed design allows the heat exchanger of the present invention to be used in situations not only where there are space or size constraints or limitations, but also“shape” limitations where a non-rectangular or non-cylindrical heat exchanger shape would be quite advantageous.

[0049] As shown by direction arrows “B₂” in FIG. 7, a relatively cold heat exchange medium, or fluid, is supplied through the tubes 14. As it will be understood, while the relatively cold fluid traverses the tubes 14, it is in a heat exchange relationship with the conductive particulates of bed 70. Further, as indicated by direction arrows “A₂” in FIG. 7, a second relatively hot heat exchange medium, or fluid, is supplied through the bed 70 in which the movement of the fluid is substantially perpendicular to the tubes 14 in a cross-flow relationship with the fluid in the tubes 14. The fluid B₂ moving through tubes 14 can be either a liquid or a gaseous material, whereas fluid A₂ would typically be a gaseous material. While the relatively hot fluid travels through the bed 70, it is in a heat exchange relationship with the tubes 14. According to an important aspect of the invention, and because the particulates have significant thermally conductive qualities, heat is readily conducted from the relatively hot first fluid A₂ across the bed 70 to the walls of the tubes 14 in a direction (as indicated by arrows “Z₂”) substantially transverse to the direction of fluid flow A₂ of the relatively hot fluid. It will be understood that the relative temperatures of the fluids could easily be reversed in which fluid A₂ was at a temperature lower than fluid B₂, without departing from the principles of the present invention. In this circumstance, the direction of heat transfer indicated by the arrows “Z₂” would be reversed from that depicted in FIG. 7.

[0050] Accordingly, heat exchangers constructed according to the principles of the present invention are characterized by flexibility of design and are capable of being constructed in various shapes and sizes not feasible with conventional fin surface systems, so as to meet unique space and performance requirements. For example, as shown in FIG. 4, a heat exchanger 30 may include several substantially cylindrical coaxial beds of conductive particulates 34 instead of an array of superposed parallel plates. As shown by direction arrows “G” in FIG. 4, a relatively cold heat exchange medium, or fluid, is supplied through the tubes 14. While the relatively cold fluid traverses the tubes 14, it is in a heat exchange relationship with the conductive particulates of beds 34. Further, as indicated by direction arrows “E”, a second relatively hot heat exchange medium, or fluid, is supplied through the beds in which the movement of the fluid is substantially perpendicular to the tubes 14 in a cross-flow relationship before exiting the heat exchanger (see direction arrows “F”). According to an important aspect of the invention, heat is readily conducted from the relatively hot first fluid E across the beds 34 to the walls of the tubes 14 in a direction (as indicated by arrows “Y”) substantially transverse to the direction of fluid flow E of the relatively hot fluid. The fluid G moving through tubes 14 can be either a liquid or a gaseous material, whereas fluid E would typically be a gaseous material. It will be understood that the relative temperatures of the fluids could easily be reversed in which fluid E was at a temperature lower than fluid G, without departing from the principles of the present invention. In this circumstance, the direction of heat transfer indicated by the arrows Y would be reversed from that depicted in FIG. 4.

[0051] Another example of a possible configuration of a heat exchanger constructed according to the present invention is illustrated in FIG. 5, depicting a conical heat exchanger generally indicated by the reference numeral 50 preferably which includes a substantially conical double screen shell 52 that confines a volume of thermally conductive particulates 11 and a substantially spiral shaped tube 56 disposed within the double screen conical shell 52. Preferably, double screen conical shell 52 comprises two coaxial conical screens 53 with the space formed therebetween being filled with conductive particulates 11. As shown by direction arrows “I” and “J” in FIG. 5, a relatively cold heat exchange medium, or fluid, is supplied through the tube 56. While the relatively cold fluid traverses the tube 56, it is in a heat exchange relationship with the conductive particulates in the double screen conical shell 52. Further, as indicated by direction arrows “H”, a second relatively hot heat exchange medium, or fluid, is supplied through the beds in which the movement of the fluid is substantially perpendicular to the tube 56 in a cross-flow relationship. According to an important aspect of the invention, heat is readily conducted from the relatively hot fluid H across the conical bed to the walls of the tube 56 in a direction (as indicated by arrows “X”) substantially transverse to the direction of fluid flow H of the relatively hot fluid. The fluid I moving through tube 56 can be either a liquid or a gaseous material, whereas fluid H would typically be a gaseous material. It will be understood that the relative temperatures of the fluids could easily be reversed in which fluid H was at a temperature lower than fluid I, without departing from the principles of the present invention. In this circumstance, the direction of heat transfer indicated by the arrows X would be reversed from that depicted in FIG. 5.

[0052] Another alternative example of a heat exchanger 60 constructed according to the present invention is illustrated in FIG. 6 that includes a substantially disc-shaped double screen shell 62 that confines a volume of conductive particulates 11. A substantially spiral shaped tube 66 is disposed within the double screens of the disc-shaped shell 62 and within the bed of conductive particulates. As shown by direction arrows “K” and “L” in FIG. 6, a relatively cold heat exchange medium, or fluid, is supplied through the tube 66. While the relatively cold fluid circulates through the tube 66, it is in a heat exchange relationship with the conductive particulates in the shell 62. Further, as indicated by direction arrows “P”, a second relatively hot heat exchange medium, or fluid, is supplied through the beds in which the movement of the fluid is substantially perpendicular to the tube 66 in a cross-flow relationship. According to an important aspect of the invention, heat is readily conducted from the relatively hot fluid P across the particulates to the walls of the tube 66 in a direction (as indicated by arrows “W”) substantially transverse to the direction of fluid flow P of the relatively hot fluid. The fluid K moving through tube 66 can be either a liquid or a gaseous material, whereas fluid P would typically be a gaseous material. It will be understood that the relative temperatures of the fluids could easily be reversed in which fluid P was at a temperature lower than fluid K, without departing from the principles of the present invention. In this circumstance, the direction of heat transfer indicated by the arrows W would be reversed from that depicted in FIG. 6.

[0053] It will be understood that all of the foregoing alternative configurations of the cross-flow particulate bed heat exchanger operate in a substantially similar manner to the cross-flow heat exchanger comprising a plurality of superposed parallel beds of conductive particulates described in detail hereinabove and as depicted in FIG. 3. Specifically, all of the foregoing alternative configurations include, similar to the heat exchanger of superposed parallel beds, a relatively cold heat exchange medium, or fluid, supplied through a series of tubes 14 disposed within at least one bed of confined conductive particulates 11. In each configuration, while the relatively cold fluid (e.g., either a liquid or a gas) is within the tubes, it is in such a position so as to be in a heat exchange relationship with the various beds of conductive particulates. Further, in each configuration, a relatively hot heat exchange medium, or fluid (e.g., typically a gas), is supplied through the various particulate beds substantially perpendicular to the tubes in a cross-flow relationship with the fluid in the tubes.

[0054] Preferably, in all of the alternative configurations of the heat exchangers, the particulate beds are confined by appropriate screens in order to confine the flakes in the bed as well as permitting fluid flow therethrough. In addition, portions of the particulate bed are bounded by tube walls at the boundary between the bed and the tubes. In addition, it will be understood that one or more walls of the bed may comprise a solid wall in order to block fluid flow in certain directions and to encourage fluid flow in a predetermined direction.

[0055] Preferably, the confining screens should have mesh size small enough to prevent particulate loss from the bed, but should have mesh size large enough so as to provide minimum obstruction to the fluid flow. Such a configuration results in only a minimal pressure drop. For example, standard aluminum window screen (16-mesh nominal) has been successfully used to date for confining the flakes. This size screen has an openness of about 70%, and is readily commercially available and inexpensive. It will be understood that other mesh sizes and screening materials can be used, as appropriate. Because the various beds of particulates in each cross flow configuration of the heat exchanger of the present invention have significant conductive qualities, heat is readily conducted from the relatively hot first fluid across the particulate bed to the walls of the tubes in a direction substantially transverse to the direction of fluid flow of the relatively hot fluid. All of the foregoing configurations of the cross flow heat exchanger of the present invention are characterized by substantially negligible resistance to heat conduction between the particulate beds and the relatively hot fluid. As a result, the cross-flow heat exchanger of the present invention is capable of heat transfer in a more efficient manner than traditional prior art extended surface heat exchangers. It will be further understood that the heat exchange fluids could also be reversed with regard to their relative temperatures in all embodiments.

[0056] As shown in FIG. 8, and in a further alternate embodiment of the present invention, a gas-gas counter-flow recuperative heat exchanger, indicated generally by the reference numeral 100, is provided and includes several substantially parallel, preferably vertically disposed, plate beds 102. Each plate bed 102 includes a pair of spaced-apart substantially parallel walls 108 separated by a volume of thermally conductive particulates 103. Preferably, each bed 102 is separated from an adjacent bed by a parallel wall 108 of an adjacent bed. It should be appreciated that the direction of flow in each bed is counter to the direction of flow in adjacent beds.

[0057] Preferably, the conductive particulates 103 comprise aluminum flakes produced by a rapid solidification process which produces a fine grain structured body identical to the particulates described hereinabove. Additionally, since the particulates preferably are not sintered or otherwise bonded, the choice of materials for the particulates is not restricted by the requirements of bondability. The aluminum flake bed material provides very high thermal conductivity within each flake, high voidage, high surface area to volume ratio, and relatively good corrosion resistance. As a result, the aluminum flakes achieve substantially instantaneous temperature equilibrium. In addition to aluminum, it is within the scope of the invention to use other materials having similar properties, such as other metals, including stainless steel.

[0058] As shown in FIG. 8, the heat exchanger 100 includes a plurality of gas plenums 106 a and 106 b, each of the plenums 106 a and 106 b being in communication with an end of a corresponding bed 102. Each bed 102 is in communication with a plenum 106 a at an end opposite that of the plenum 106 b of an adjacent bed 102. Plenums 106a on a first side 105 of the heat exchanger 100 are connected to a gas inlet that supplies relatively cold gas to the plenums on the first side of the heat exchanger at the arrows M₁. Plenums 106 b on an opposite second side 107 of the heat exchanger 100 are connected to a gas inlet that supplies relatively hot gas to the plenums 106 b on the second opposite side 107 of the heat exchanger at the arrows N₁.

[0059] Preferably, the plurality of parallel plate beds of conductive particulates includes a solid top plate (not shown in FIG. 8) and a solid bottom plate 110. Preferably, the solid top plate is connected to the heat exchanger 100 in a gas-tight manner. Additionally, the bottom plate 110 preferably also comprises a gas-tight bottom layer of the plenums 106. Preferably, the parallel plate beds 102 include first and second ducting ends 112 a and 112 b which comprise screens 114 that permit fluid flow therethrough. Additionally, the screens 114 and plates advantageously retain the conductive particulates.

[0060] As it will be understood, when the relatively cold gas is supplied in the plenums on the first side of the heat exchanger 100 (see direction arrows M₁), the relatively cold gas passes through a corresponding first ducting end 112 a, through the length of a corresponding bed of particulates 102, and out a corresponding second ducting end 112 b (see direction arrows M₂). Similarly, when the relatively hot gas is supplied in the plenums 106 on the second opposite side of the heat exchanger 100 (see direction arrows N₁), the relatively hot gas passes through a corresponding first ducting end 112 a, through the length of a corresponding bed of particulates 102, and out a corresponding second ducting end 112 b (see direction arrows N₂). It will be understood that the relatively hot gas and the relatively cold gas flow in opposite directions in adjacent beds in a counter-flow relationship. It will be further understood that the heat exchange fluids could also be reversed with regard to their relative temperatures. This counter flow arrangement permits the two gas streams to approach the same temperature at each point in the passage. Thus, this arrangement tends to the highest heat transfer efficiency possible depending upon the bed dimensions and flow velocities.

[0061] It should be noted that while the relatively hot and relatively cold gases are flowing through the beds 102 in a counter-flow relationship they are in a heat exchange relationship with the particulates 103. According to an important aspect of the invention, and because the beds 102 of particulates have significant thermally conductive qualities, heat is readily conducted from the relatively hot first gas across the beds 102 to the walls 108 of the beds 102 in a direction substantially transverse to the direction of fluid flow of the relatively hot gas, as indicated by arrows “V”.

[0062] As shown in FIG. 9, and in an further alternate embodiment of the present invention, a liquid-gas counter-flow recuperative heat exchanger, indicated generally by the reference numeral 200, is provided and includes several substantially parallel, preferably vertically disposed, plate beds 202 a, 202 b. A first group of alternating plate beds 202 a includes a pair of spaced-apart substantially parallel walls 208 separated by a volume of thermally conductive particulates 203. A second group of alternating plate beds 202 b similarly includes a pair of spaced-apart substantially parallel walls 208. Preferably, each bed 202 is separated from an adjacent bed by a parallel wall 208 of an adjacent bed. It should be appreciated that the direction of flow in each bed is counter to the direction of flow in adjacent beds. Preferably the conductive particulates 203 comprise aluminum flakes produced by a rapid solidification process which produces a fine grain structured body identical to the particulates described hereinabove.

[0063] Similar to the gas-gas counter-flow heat exchanger described above, and as shown in FIG. 9, the heat exchanger 200 includes a plurality of gas plenums 206, each of the plenums 206 being in communication with an end of one of the first group of beds 202 containing the conductive particulates. Plenums 206 on a first side 205 (in FIG. 9) of the heat exchanger 200 are connected to a gas inlet that supplies relatively hot gas to the plenums of the first side of the heat exchanger at the arrows Q₁. A fluid inlet on an opposite “far” side 207 of the heat exchanger 200 supplies relatively cold fluid through each of the second group of parallel plate beds that are do not contain particulates, as indicated by arrows R. Preferably, the fluid travels in the vertical space formed between the vertical walls of each of the second group of plate beds. Alternatively, the fluid travels through the second group of parallel plate beds through an array of tubes held in place between the vertical walls of each of the second group of plate beds with baffles.

[0064] Preferably, the plurality of parallel plate beds includes a solid top plate (not shown in FIG. 9) and a solid bottom plate 210. Preferably, the solid top plate is connected to the heat exchanger in a gas-tight manner. Additionally, the bottom plate 210 preferably also comprises a gas-tight bottom layer of the plenums 206. Preferably, each of the first group of parallel plate beds 202 include first and second ducting ends 212 a and 212 b which comprise screens 214 that permit fluid flow therethrough. Additionally, the screens 214 and plates advantageously contain the conductive particulates within each of the first group of parallel plate beds.

[0065] As it will be understood, when the relatively hot gas is supplied in the plenums on the first side of the heat exchanger 200 (see direction arrows Q₁), the relatively cold gas passes through a corresponding first ducting end 212 a, through the length of a corresponding bed of particulates 202, and out a corresponding second ducting end 212 b (see direction arrows Q₂). Similarly, when the relatively cold fluid is supplied to each of the second group of beds from the second opposite side of the heat exchanger 200 (see direction arrows R), the relatively cold fluid passes through the length of a corresponding bed. It will be understood that the relatively hot gas and the relatively cold fluid flow in opposite directions in adjacent beds in a counter-flow relationship. It will be further understood that the heat exchanger fluids could also be reversed with regard to their relative temperatures. This counter-flow arrangement permits the two fluid streams to approach the same temperature at each point in the passage. Thus, this arrangement tends to the highest heat transfer efficiency possible depending upon bed dimensions and flow velocities.

[0066] It should be appreciated that while the relatively hot gas and relatively cold fluid are flowing through the beds in a counter-flow relationship that they are in a heat exchange relationship. According to an important aspect of the invention, and because the beds of particulates have significant thermally conductive qualities, heat is readily conducted from the relatively hot gas across the beds to the walls of the beds in the direction substantially transverse to the direction of fluid flow of the relatively cold fluid, as indicated by arrows “S”.

[0067] In a conventional prior art extended surface heat exchanger, as shown in FIG. 2, heat is transferred from the relatively hot fluid (see direction arrow A₁) to fins 17 across a somewhat conductively resistant boundary layer or film of fluid adjacent to the fins 17. In contrast, the above-described embodiments of the heat exchanger of the present invention is characterized by substantially negligible resistance to heat conduction between the particulate beds 102 and the relatively hot gas. As a result, the counter-flow heat exchanger of the present invention is also capable of heat transfer in a more efficient manner than traditional prior art extended surface heat exchangers.

[0068] As best shown in FIG. 10, one or more of the substantially parallel plate beds 202 described above with reference to the counter-flow recuperative heat exchangers, may comprise a folded bed of 300 conductive metal particulates. As shown in FIG. 10, the folded bed preferably comprises several lateral folds 302 to result in an accordion-like configuration. Such an arrangement results in several “V-shaped” wedges 304 of conductive metal particulate beds through which fluid flows (see direction arrows V). Preferably the folded bed comprises one or more screens, similar to those described hereinabove, the screens being of an appropriate mesh to contain the folded layers of particulates therebetween. The advantages of this configuration include providing a relatively large amount of flow area in a limited frontal surface area. Additionally, such an arrangement would advantageously reduce flow velocity and, hence, would reduce undesirable pressure drop when used in the counter-flow systems described hereinabove.

[0069] According to an important aspect of the invention, and as best shown in FIG. 11, in the various alternative configurations of the invention and especially in the previously described counter-flow heat exchangers, the beds of conductive particulates may further comprise a plurality of transverse spacers 316 that connect the “primary” walls 318 of each plate bed 202. Preferably, these spacers substantially compartmentalize each parallel plate bed into several adjacent and longitudinally disposed flow channels. As should be appreciated, this configuration increases the overall available wall area for dissipating heat in a given length of the bed. As a result, heat may be even more rapidly transferred from a fluid passing through the particulates either directly to the primary walls (see arrows U₁) or to the spacers first, and then through conduction, to the primary walls (see arrows U₂).

[0070] Alternatively, in order to compartmentalize each bed 202 into separate flow channels, corrugated walls 320 (see FIG. 12) may be used to increase the overall area of heat dissipating wall area in a given space. In this circumstance, heat is conducted in essentially four directions directly to the walls (see arrows T). Preferably, in this configuration, the walls are doubly corrugated and have a plurality of aligned “V” shaped corrugations 324 so that longitudinal compartments of substantially diamond-shaped cross section are formed. Similar to the spacer configuration described above, each of the diamond-shaped flow channels that result from the corrugated wall configuration encloses a volume of conductive metal particulates. As a result, heat may be more rapidly transferred from a fluid passing through the particulates because there is an overall greater wall area for dissipating heat in a given space.

[0071] In summary, numerous benefits have been described which result from employing the concepts of the invention. Both the illustrated cross-flow and counter-flow embodiments of the recuperative heat exchanger of the present invention are capable of being manufactured more efficiently than traditional extended surface heat exchangers that require extensive sintering or brazing operations during manufacture. The heat exchanger of the present invention is characterized by design flexibility and is capable of being constructed in various shapes and sizes to meet unique space and performance requirements. Finally, the metal particulates of the heat exchanger of the present invention have significant thermally conductive qualities that allow for the efficient transfer of heat between the heat exchange fluids and the particulates without significant resistance to heat conduction through any type of boundary layer or film of fluid therebetween.

[0072] The foregoing description of a preferred embodiment of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiment was chosen and described in order to best illustrate the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appending claims when interpreted in accordance with the breadth to which they are fairly, legally and equitably entitled. 

What is claimed is:
 1. A recuperative non-fluidized heat exchanger comprising: (A) at least one bed of unbonded confined conductive particulates, each of said beds having a plurality of walls, each of said beds having a thickness sufficient to permit fluid flow therethrough without substantial resultant pressure drop; (B) at least one tube being longitudinally disposed in each of said beds, each tube having a diameter sufficient to permit fluid flow therethrough; and (C) a first fluid of a first temperature directed through said at least one bed of confined particulates, said confined particulates remaining substantially stationary with respect to said walls and to each other when said first fluid is directed through said bed, a second fluid of a second temperature directed through said at least one tube, thereby causing heat to be conducted between said first and second fluids across said at least one confined bed to the walls of said tubes in a direction substantially transverse to the direction of fluid flow of both said fluids.
 2. The heat exchanger of claim 1, wherein said particulates are characterized by a high surface area to bulk volume ratio.
 3. The heat exchanger of claim 1, wherein said particulates are not sintered or otherwise bonded.
 4. The heat exchanger of claim 1, wherein said particulates comprise aluminum flakes, and each said flake having a thickness of about 0.001 to about 0.02 inches and a length and width ranging from about 0.04 to about 0.15 inches.
 5. The heat exchanger of claim 1, wherein said particulates have a solidity fraction of about 0.085 to about 0.35.
 6. The heat exchanger of claim 1, wherein said walls of said beds comprise screens, and wherein said particulates are substantially confined by said screens, said screens having a mesh size permitting fluid flow therethrough.
 7. The heat exchanger of claim 1, wherein heat transfer between said first fluid and said particulates of said at least one bed is characterized by negligible resistance to heat conduction therebetween.
 8. The heat exchanger of claim 1, wherein said at least one bed comprises an array of stacked parallel layers of superposed beds, said array having a substantially cubic configuration.
 9. The heat exchanger of claim 8, wherein pairs of adjacent beds of said array of superposed beds are linked together in a spaced-apart relationship by at least one end plate.
 10. The heat exchanger of claim 8, wherein each bed of said array of superposed beds is separated by a passage, said passage being of sufficient dimensions to permit fluid flow therethrough.
 11. The heat exchanger of claim 1, wherein said at least one tube comprises a plurality of spaced-apart parallel tubes.
 12. A recuperative heat exchanger comprising: (A) a plurality of substantially cylindrical beds of confined conductive particulates, each of said beds comprising first and second cylindrical walls, each said first cylindrical wall having a substantially circular cross-section of a first wider diameter, each said second cylindrical wall having a substantially circular cross-section of a second diameter, each said second cylindrical wall being coaxially disposed within said first cylindrical wall, each of said beds comprising a substantially cylindrical layer of thermally conductive particulates contained in a space defined by said first and second cylindrical walls, and each bed of said plurality of cylindrical beds having a different cross-sectional diameter; (B) at least one tube having a diameter sufficient to permit fluid flow therethrough; (C) a first fluid of a first temperature directed through said beds of confined particulates, a second fluid of a second temperature directed through said at least one tube, thereby causing heat to be conducted between said first and second fluids across said beds to the walls of said at least one tube in a direction substantially transverse to the direction of fluid flow of both fluids.
 13. The heat exchanger of claim 12, wherein said at least one tube comprises a substantially spiral-shaped tube disposed within each bed of confined conductive particulates.
 14. The heat exchanger of claim 12, wherein said at least one tube comprises a plurality of longitudinally disposed tubes, said tubes being positioned within said conductive particulate beds substantially parallel to the longitudinal axis of said heat exchanger.
 15. The heat exchanger of claim 12, wherein said particulates are characterized by a high surface area to bulk volume ratio.
 16. The heat exchanger of claim 12, wherein said particulates are not sintered or otherwise bonded.
 17. The heat exchanger of claim 12, wherein said particulates comprise aluminum flakes, and each said flake having a thickness of about 0.001 to about 0.02 inches and a length and width ranging from about 0.04 to about 0.15 inches.
 18. The heat exchanger of claim 12, wherein said particulates have a bulk density of about 0.23 to about 0.95 grams per cubic centimeter.
 19. The heat exchanger of claim 12, wherein said walls of said beds comprise screens, and wherein said particulates are substantially confined by said screens, said screens permitting fluid flow therethrough.
 20. The heat exchanger of claim 12, wherein heat transfer between said first fluid and said particulates of said at least one bed is characterized by negligible resistance to heat conduction therebetween.
 21. A recuperative heat exchanger comprising: (A) at least one bed of confined conductive particulates, each of said beds comprising a substantially conical shell, said shell confining a volume of conductive particulates; (B) at least one substantially spiral-shaped tube disposed about the periphery of said conical shell; (C) a first fluid of a first temperature directed through said at least one bed of confined particulates, a second fluid of a second temperature directed through said at least one tube, thereby causing heat to be conducted between said first and second fluids across said at least one confined bed to the walls of said at least one tube in a direction substantially transverse to the direction of fluid flow of both said fluids.
 22. The heat exchanger of claim 21, wherein said particulates are characterized by a high surface area to bulk volume ratio.
 23. The heat exchanger of claim 21, wherein said particulates are not sintered or otherwise bonded.
 24. The heat exchanger of claim 21, wherein said particulates comprise aluminum flakes, and each said flake having a thickness of about 0.001 to about 0.02 inches and a length and width ranging from about 0.04 to about 0.15 inches.
 25. The heat exchanger of claim 21, wherein said particulates have a bulk solidity fraction of about 0.085 to about 0.35.
 26. The heat exchanger of claim 21, wherein heat transfer between said first fluid and said particulates of said at least one bed is characterized by negligible resistance to heat conduction therebetween.
 27. The heat exchanger of claim 21, wherein said conical shell comprises screens, and wherein said particulates are substantially confined by said screens, said screens permitting fluid flow therethrough.
 28. The heat exchanger of 21, wherein the path of said spiral shaped tube substantially defines a cone-shaped surface.
 29. A recuperative heat exchanger comprising: (A) at least one bed of confined conductive particulates, each of said beds comprising a substantially disc-shaped shell, said shell confining a volume of conductive particulates; (B) at least one substantially spiral-shaped tube disposed within said disc-shaped shell; (C) a first fluid of a first temperature directed through said at least one bed of confined particulates, a second fluid of a second temperature directed through said at least one tube, thereby causing heat to be conducted between said first and second fluids across said at least one confined bed to the walls of said at least tube in a direction substantially transverse to the direction of fluid flow of both fluids.
 30. The heat exchanger of claim 29, wherein said disc-shaped shell comprises screens, and wherein said particulates are substantially confined by said screens, said screens permitting fluid flow therethrough.
 31. The heat exchanger of claim 29, wherein said particulates are characterized by a high surface area to bulk volume ratio.
 32. The heat exchanger of claim 29, wherein said particulates are not sintered or otherwise bonded.
 33. The heat exchanger of claim 29, wherein said particulates comprise aluminum flakes, and each said flake having a thickness of about 0.001 to about 0.02 inches and a length and width ranging from about 0.04 to about 0.15 inches.
 34. The heat exchanger of claim 29, wherein said particulates have solidity fraction of about 0.085 to about 0.35.
 35. The heat exchanger of claim 29, wherein heat transfer between said first fluid and said particulates of said at least one bed is characterized by negligible resistance to heat conduction therebetween.
 36. The heat exchanger of claim 1, wherein said at least one bed comprises a relatively thin contoured shell configured to a similarly contoured surface area.
 37. A recuperative heat exchanger comprising: (A) a plurality of substantially parallel plate beds, each of said plate beds comprising of a pair of spaced walls, each of said walls being separated by a volume of conductive metal particulates therebetween, each of said plate beds having a thickness sufficient to permit fluid flow therethrough without substantial resultant pressure drop; (B) a plurality of gas plenums, each of said plenums being in communication with one end of a corresponding said plate bed, and wherein adjacent plate beds are in communication with one of said plenums at an end opposite to one of said plenums of an adjacent plate bed; (C) a first fluid of a first temperature directed through said plenums on a first side of said heat exchanger, a second fluid of a second temperature directed through said plenums on a second side of said heat exchanger, said second side being opposite said first side of said heat exchanger, thereby causing a first gas stream to flow between a first group of alternating pairs of plates in one direction, and a second gas stream to flow through a second group of alternating pairs of plates in an opposite direction parallel to the gas flow in said first group to plate pairs, and causing heat to be conducted from said relatively hot first gas across said particulate beds to the walls of said parallel plates in a direction substantially transverse to the direction of gas flow.
 38. The heat exchanger of claim 37, wherein said particulates are characterized by a high surface area to bulk volume ratio.
 39. The heat exchanger of claim 37, wherein said particulates are not sintered or otherwise bonded.
 40. The heat exchanger of claim 37, wherein said particulates comprise aluminum flakes, and each said flake having a thickness of about 0.001 to about 0.02 inches and a length and width ranging from about 0.04 to about 0.15 inches.
 41. The heat exchanger of claim 37, wherein said particulates have a solidity fraction of about 0.085 to about 0.35.
 42. The heat exchanger of claim 37, wherein said parallel plate beds further include a solid top plate and a solid bottom plate, said parallel plate beds each including first and second ducting ends, each of said ducting ends comprising a screen which permits fluid flow therethrough.
 43. The heat exchanger of claim 37, wherein one or more of said substantially parallel plate beds comprises a pair of spaced substantially parallel walls having a folded bed of conductive metal particulates therebetween, said folded bed comprising one or more screens, said screens being of an appropriate mesh to contain a layer of said particulates therebetween, said folded bed comprising a plurality of lateral folds.
 44. The heat exchanger of claim 37, wherein said pair of spaced walls of one or more of said plate beds further comprises a plurality of conductive spacers connectedly disposed therebetween.
 45. The heat exchanger of claim 37, wherein each wall of said pair of spaced walls of one or more of said plate beds is substantially corrugated.
 46. The heat exchanger of claim 45, wherein said corrugated walls include a plurality of “V” shaped corrugations, said “V” shaped corrugations further being aligned so as to divide said volume of conductive metal particulates into compartments of substantially diamond-shaped cross section.
 47. A recuperative heat exchanger comprising: (A) a plurality of substantially parallel plate beds, each of said plate beds comprising a pair of spaced walls, each of a first group of alternating pairs of spaced parallel walls being separated by a volume of conductive metal particulates therebetween, each of a second group of alternating pairs of spaced parallel walls having a substantially void space therebetween, each of said plate beds having a thickness sufficient to permit fluid flow therethrough without substantial resultant pressure drop; (B) a plurality of gas plenums, each of said plenums being in communication with one end of one of said first group of alternating pairs of spaced parallel walls, wherein alternating plate beds are in communication with one of said plenums; (C) a first fluid of a first temperature directed through said plenums on a first side of said heat exchanger, a second fluid of a second temperature directed through each of said second group of alternating pairs of spaced parallel walls having a substantially void space therebetween on a second side of said heat exchanger, said second side being opposite said first side of said heat exchanger, thereby causing a first gas stream to flow between a first fluid stream to flow between a first group of alternating pairs of plates in one direction, and a second fluid stream to flow through a second group of alternating pairs of plates in an opposite direction parallel to the gas flow in said first group to plate pairs, and causing heat to be conducted from said relatively hot first fluid across said particulate beds to the walls of said parallel plates in a direction substantially transverse to the direction of gas flow.
 48. The heat exchanger of claim 47, wherein said particulates are characterized by a high surface area to bulk volume ratio.
 49. The heat exchanger of claim 47, wherein said particulates are not sintered or otherwise bonded.
 50. The heat exchanger of claim 47, wherein said particulates comprise aluminum flakes, and each said flake having a thickness of about 0.001 to about 0.02 inches and a length and width ranging from about 0.04 to about 0.15 inches.
 51. The heat exchanger of claim 47, wherein said particulates have a solidity fraction of about 0.085 to about 0.35.
 52. The heat exchanger of claim 47, wherein said parallel plate beds further include a solid top plate and a solid bottom plate, said parallel plate beds each including first and second ducting ends, each of said ducting ends comprising a screen which permits fluid flow therethrough.
 53. The heat exchanger of claim 47, wherein one or more of said substantially parallel plate beds comprises a pair of spaced substantially parallel walls having a folded bed of conductive metal particulates therebetween, said folded bed comprising one or more screens, said screens being of an appropriate mesh to contain a layer of said particulates therebetween, said folded bed comprising a plurality of lateral folds.
 54. The heat exchanger of claim 47, wherein said pair of spaced walls of one or more of said plate beds further comprises a plurality of conductive spacers connectedly disposed therebetween.
 55. The heat exchanger of claim 47, wherein each wall of said pair of spaced walls of one or more of said plate beds is substantially corrugated.
 56. The heat exchanger of claim 55, wherein said corrugated walls include a plurality of “V” shaped corrugations, said “V” shaped corrugations further being aligned so as to divide said volume of conductive metal particulates into compartments of substantially diamond-shaped cross section. 